The present invention relates to flexible sheet or roll stock film having elastic characteristics and to products formed of such film. Film-forming polymers are used to hot form the film with elastic and nonelastic or inelastic discrete polymer portions connected at a joint therebetween.
The films are useful in tapes, closure devices, labels and other constructions requiring a stretchable or elastic film element. The shear resistance and elastic property of the film in combination with the non-creep nature of the inelastic portions provide unique and valuable performance useful in a wide range of applications. The films may be used as a construction film for forming an element of a more comprehensive tape or closure system including industrial or craft applications requiring pieces to be secured together with tension during a dry cycle or medical applications such as medical tapes, suture tapes, nasal dilators, bandages and the like.
The films are particularly useful as substrates for closure systems such as mechanical and/or self-adhesive diaper fastening tapes or tabs. In such applications, the elastic characteristic of the film enhances fit, comfort, absorbency, containment and/or security of closure. The films may also be used as attachments to the waist or leg areas of a device or article of clothing for enhancing fit, comfort, and/or sealing characteristics. The film is especially useful in connection with disposable diaper tape fastening systems, and it is specifically described with respect to the same hereinafter.
Disposable diapers are known in the art and comprise multiple layer assemblies or laminates including an inner filling of absorbent fiber or material sandwiched between outer layers. One of the outer layers includes an absorbent material to be disposed against the user, and the other outer layer may comprise a waterproof plastic film for containment of waste within the diaper.
The use of stretchable fastening tapes or tabs in disposable diapers is disclosed in U.S. Pat. No. 3,800,796 to Jacobs. In Jacobs, a polymeric variation of the tape includes a semielastic strip having a fully extensible elastic central segment and two non-extensible inelastic terminal segments. The elastic segment comprises a heat-sealable elastomer such as a butadiene-styrene block polymer. The patent does not describe a coextrusion process for making film that may be used to form the tape.
U.S. Pat. No. 4,787,897 to Torimae et al. discloses a co-extruded diaper fastening tape with an elastic central segment and nonelastic terminal segments. The elastic segment includes triblock polymers containing 10 to 80 parts of a processing aid comprising a hydrogenated terpene resin or alicyclic hydrocarbon having a melt or softening point of 80.degree. C. and a molecular weight of 400 to 2000.